The long-term goal of this project is to better understand the biological properties of corneal and conjunctival epithelial stem cells. Information about the location and properties of these stem cells is central to understanding the mechanisms involved in the maintenance and differentiation of these epithelia. The focus of this grant is to further define the stem and transient amplifying cell populations in corneal epithelium. In addition, in view of the intimate relationship between corneal and conjunctival epithelia, we will extend some of these investigations to include conjunctival epithelium. During this grant period we will use a combination of light and transmission electron microscopy, cell and organ culture, and tissue section autoradiography to study these problems using SENCAR mice and rabbits as experimental animals. We will: 1. further define the differences in the proliferative potential of limbal, peripheral and central corneal epithelia; 2. determine the rate and driving force for centripetal migration in normal corneal epithelium; 3. define the cell cycle phase durations in limbal, peripheral and central corneal epithelia; 4. determine whether during vitamin A deficiency the keratinized conjunctival epithelium is limbal-derived; and 5. study the location of "label-retaining cells" in conjunctival epithelium. Information from these studies should lead to a better understanding of the roles of the limbal and corneal epithelia in growth control and differentiation. It should also lead to a better understanding of the interrelationship between conjunctival and corneal epithelia. This will ultimately increase our knowledge on diseases of the ocular surface epithelia such as persistent corneal epithelial defect and the various dry- eye conditions.